As mobile devices have been increasingly developed, and the demand for such mobile devices has increased, the demand for secondary batteries has also sharply increased. Among such secondary batteries is a lithium secondary battery exhibiting high energy density and operating voltage and excellent preservation and service-life characteristics, which has been widely used as an energy source for various electronic products as well as for the mobile devices.
Depending upon kinds of external devices in which secondary batteries are used, the secondary batteries may be used in the form of a single battery or in the form of a battery pack having a plurality of unit cells electrically connected to one another. For example, small-sized devices, such as mobile phones, can be operated for a predetermined period of time with the power and the capacity of one battery. On the other hand, a battery pack needs to be used in middle or large-sized devices, such as laptop computers, portable digital versatile disc (DVD) players, small-sized personal computers (PCs), electric vehicles and hybrid electric vehicles, because high power and large capacity are necessary for the middle or large-sized devices.
A battery pack is manufactured by connecting a protection circuit to a core pack having a plurality of unit cells connected in series and/or in parallel to each other. In a case in which prismatic batteries or pouch-shaped batteries are used as the unit cells, the prismatic batteries or the pouch-shaped batteries are stacked so that large-sized surfaces of the prismatic batteries or the pouch-shaped batteries face each other, and then electrode terminals of the prismatic batteries or the pouch-shaped batteries are connected to each other by connecting members, such as bus bars. In a case in which a three-dimensional battery pack having a hexahedral structure is to be manufactured, therefore, the prismatic batteries or the pouch-shaped batteries are preferably used as unit cells of the battery pack.
On the other hand, cylindrical batteries generally have larger electric capacities than the prismatic batteries or the pouch-shaped batteries. However, it is difficult to arrange the cylindrical batteries in a stacked structure due to the external shape of the cylindrical batteries. In a case in which a battery pack is configured generally in a line type structure or in a plane type structure, though, the cylindrical batteries are structurally more advantageous than the prismatic batteries or the pouch-shaped batteries.
Consequently, a battery pack having a plurality of cylindrical batteries connected in parallel and series to each other is widely used in laptop computers, portable DVD players, and portable PCs. The battery pack may be configured in various core pack structures. For example, the core pack of the battery pack may be generally configured in a 2P (parallel)-3S (series) line type structure, a 2P-3S plane type structure, a 2P-4S line type structure or a 2P-4S plane type structure.
The parallel connection structure is achieved by arranging two or more cylindrical batteries in the lateral direction thereof so that the cylindrical batteries are adjacent to each other in a state in which electrode terminals of the cylindrical batteries are oriented in the same direction and connecting the electrode terminals of the cylindrical batteries to each other via connecting members by welding. The cylindrical batteries connected in parallel to each other may be referred to as a “bank.”
The series connection structure is achieved by arranging two or more cylindrical batteries in the longitudinal direction thereof so that electrode terminals of the cylindrical batteries having opposite polarities are successively disposed one after another, or arranging two or more cylindrical batteries in the lateral direction thereof so that the cylindrical batteries are adjacent to each other in a state in which electrode terminals of the cylindrical batteries are oriented in opposite directions, and connecting the electrode terminals of the cylindrical batteries to each other via connecting members by welding.
The electrical connection between the cylindrical batteries is generally achieved by spot welding using thin plane type connecting members, such as nickel plates. Also, a protection circuit is connected to a core pack manufactured by connecting cylindrical batteries in parallel and/or in series to each other to manufacture a battery pack.
FIGS. 1 to 3 typically illustrate a series of processes to manufacture a core pack configured in a 2P-3S plane type structure using a conventional plane type connecting member.
Referring first to FIGS. 1 and 2, in order to manufacture a core pack 50 configured in a 2P-3S plane type structure, a total of 6 cylindrical batteries 10, as unit cells, are arranged in the lateral direction thereof to form three banks 11, 12 and 13.
In order to manufacture the core pack 50, first, the first bank 11 and the third bank 13 are disposed so that cathode terminals of the first bank 11 and the third bank 13 are oriented forward, and the second bank 12 is disposed in the direction opposite to the direction in which the first bank 11 and the third bank 13 are disposed so that anode terminals of the second bank 12 are oriented forward.
Subsequently, spot welding is carried out at the fronts (see FIG. 1) of the unit cells 10 in a state in which a first connecting member 16 is placed at the cathode terminals of the first bank 11, a second connecting member 17 is placed over the anode terminals of the second bank 12 and the cathode terminals of the third bank 13, thereby achieving the coupling between the connecting members 16 and 17 and the electrode terminals located at the fronts of the unit cells 10.
Subsequently, spot welding is carried out at the rears (see FIG. 2) of the unit cells 10 in a state in which a third connecting member 18 is placed over the anode terminals of the first bank 11 and the cathode terminals of the second bank 12, and a fourth connecting member 19 is placed at the anode terminals of the third bank 13, thereby achieving the coupling between connecting members 18 and 19 and the electrode terminals located at the rears of the unit cells 10.
Referring to FIG. 3 together with FIGS. 1 and 2, the third bank 13 is perpendicularly bent forward from the middle of the second connecting member 17, and the first bank 11 is perpendicularly bent rearward from the middle of the third connecting member 18, thereby manufacturing a core pack configured in a 2P-3S plane type structure. For information, P (parallel) indicates electrical parallel connection and S (series) indicated electrical series connection.
However, plane type connecting members are generally configured in a long bar type structure. In a case in which a plurality of cylindrical batteries arranged in the lateral direction thereof so that the cylindrical batteries are adjacent to each other is connected to each other via such plane type connecting members, it is difficult to carry out welding in a state in which the plane type connecting members are correctly placed at electrode terminals disposed at the tops and bottoms of the cylindrical batteries.
Also, when two or more cylindrical batteries are arranged in the lateral direction thereof so as to be adjacent to each other in a state in which electrode terminals of the cylindrical batteries are oriented in opposite directions, the electrode a terminals of the cylindrical batteries are connected to each other via a general long bar type connecting member, and the connection portion is bent in order to connect the cylindrical batteries in series to each other, it is difficult to accurately and stably bent the cylindrical batteries in a linear series structure and the bent portion may be broken since the width and thickness of the connecting member at the bent portion are thin.
That is, in a case in which a plurality of cylindrical batteries is connected to each other using a general plane type connecting member, it is difficult and complicated to connect the cylindrical batteries, thereby greatly lowering manufacturing efficiency of a battery pack.
In connection with this case, research has been conducted on technology to improve assembly efficiency of a battery pack. For example, Japanese Patent Application Publication No. 2001-325931 discloses the structure of an assembly battery in which a plurality of cylindrical battery cells is fixed and electrically connected to each other wherein circular grooves the inner diameter of each of which is slightly greater than the outer diameter of each of the battery cells are formed based on the number of the battery cells, and opposite ends of the battery cells are vertically fitted and fixed by two holder cases, made of an electrically insulative resin material, in which metal connection members to electrically connect the battery cells to each other are buried, so that the battery cells are connected in series to each other.
In the structure of the assembly battery, however, the electrically insulative resin material in which the metal connection members are buried with the result that the volume and weight of a battery pack are increased. Consequently, the battery cell receiving space of the battery pack is reduced, and energy density of the battery pack per unit volume is lowered.
Also, Japanese Patent Application Publication No. 2001-325931 discloses a connecting member for batteries used to connect two cylindrical batteries, which are arranged in parallel to each other in the radial direction thereof in a state in which the cylindrical batteries are disposed in opposite directions, in series to each other wherein the connecting member, which is formed in a plane shape, includes a first planar connection part joined to the bottom of one of the battery cells and a second connection part extending from the first connection part, the second connection part including an opening through which a cathode terminal of the other unit cell protrude and a circular groove bottom joined to a sealing plate of the other unit cell or a planar part having a step formed between the planar part and the first connection part.
However, it is difficult to use the connecting member for batteries in a case in which three or more cylindrical batteries are connected in series to each other. Also, the connecting member includes the first connection part and the second connection part. Consequently, a process to manufacture the connecting member is complicated, and productivity of a battery pack is lowered.
Consequently, there is a high necessity for technology to easily and efficiently achieve electrical connection between battery cells, thereby improving manufacturing efficiency and productivity of a battery pack while solving the above conventional problems.